When a search keyword or a search expression is input, a document retrieving apparatus retrieves target documents and outputs retrieved documents according to ranking (for example, see Patent Document 1). It is difficult for a user to read all of many documents obtained as a retrieval result. In order to rapidly understand a summary of contents of many obtained documents (a document set), a technique of plotting each document included in the document set on two-dimensional coordinates has been suggested (for example, see Patent Document 2).
Patent Document 1: Japanese Patent Application Laid-Open No. 2005-43987
Patent Document 2: Japanese Patent Application Laid-Open No. 2003-345811
Patent Document 3: Japanese Patent Application Laid-Open No. 2002-015001